1. Field of the Invention
The invention relates to polyurethane foams which are sprayed into place, and more particularly relates to the production of sprayed polyurethane foams which have smooth surfaces due to a mono or polyamine additive.
2. Description of Related Publications
Urethane foams are frequently used as building insulation, pipe and tank insulation, roof insulation, generally for any application where it is convenient that the insulation be sprayed into place. A foam having about a three pound density is commonly used for the roof applications. Two problems arise in the production of sprayed foams, the first being that the low viscosity foam components create problems during the spray operation since the continuous phases of the rising foams, which consist of the polyol and isocyanate, have lower viscosities and thus exhibit greater tendencies to flow during rise. The tendency to flow (lateral creep) can be decreased by the use of higher catalyst levels or by the use of more active catalysts. However, this solution creates the second problem; namely, the foam will have a rough surface since the over-spray will not blend with the rising foam.
Thus, a number of criteria are important in sprayed insulation foams, which are generally considered to be rigid foams. The foam must have a good compressive strength, usually greater than 40 psi, to withstand foot traffic without damaging the foam, and the foam should have a smooth surface since protective coatings are usually required and the smoother the surface, the less coating is required to cover the foam. It has been found that the use of small amounts of primary or secondary amines in the sprayed foam formulation will accomplish the result of a smooth surface without causing a decrease in the compressive strength.
It does not seem that those skilled in the art have applied themselves to trying to create a sprayed foam having a smooth outer surface when cured. However, a number of references disclose polyurethane foam formulations which generally have amine additives for one reason or another. Tertiary amines are, of course, common polyurethane catalysts. For example, U.S. Pat. No. 3,179,606 describes the use of compounds of the general formula EQU NH.sub.2 (CH.sub.2 CH.sub.2 NH).sub.x (RO).sub.n R(NHCH.sub.2 CH.sub.2).sub.x NH.sub.2
where R is an alkene radical with 2 to 4 carbon atoms, x is an integer from 0 to 4, and n is an integer such that the polyglycol starting material used to prepare the polyamine has an average molecular weight of 400 to 2,000. This polyamine is used in the preparation of cellular polyurethane foam to rapidly attain high strength and to produce a foam having low density and a high elongation at its break point. U.S. Pat. No. 3,984,360 describes the use of polyoxyalkene primary amines of the type ##STR1## wherein x is an integer from 2 to 8, and R is hydrogen or lower alkyl. In this instance, the polyoxyalkene primary amines are used as the catalysts along with tin catalysts in the sprayed foams described therein to avoid the inclusion of lead salts. U.S. Pat. No. 4,218,543 and other patents cited therein describe the use of aryl amines in reaction injection molding systems.
A general review of the reaction of amines with isocyanates is given in "Polyurethane Chemistry and Technology, Part I," by J. H. Saunders and K. C. Frisch, Interscience Publishers (1962), pgs 65-72, 173-179. H. J. Kollmeier, et al. in "New Crosslinkers in the Development of High Resilience Polyurethane Foams," J. Cellular Plastics, (1977), pg 42, describe the use of diethanolamine to increase the stiffness of high resilience foams.
International Minerals and Chemical Corporation has recently marketed a polyurethane foam additive entitled "AMP" designed to promote a fast cream time and to serve as an HCl scavenger among other functions. Although AMP is promoted as being trifunctional with respect to the isocyanate reaction, AMP is known to be 2-amino-2-methyl-1-propanol which contains one hydroxyl group and one primary amine group for a total of two functionalities.